I'd use it for making my own SQUIDs[1], as a start. There are a number of experiments I want to do, and things I want to understand[2][3], and not having to have cryogenics keeping the detectors cold would be helpful.

I'd also like to use this for antennas, transmission lines, and tuned cavities.[4] There are a lot of things you could do at VLF frequencies[5] that require long, long wires... with lots of resistance, unless you have a defense budget, the resistance eats into efficiency. Superconductors could help deal with that.

[1] https://en.wikipedia.org/wiki/SQUID

[2] https://en.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect

[3] https://en.wikipedia.org/wiki/Longitudinal_wave#Electromagne...

[4] https://en.wikipedia.org/wiki/Superconducting_radio_frequenc...

[5] https://en.wikipedia.org/wiki/Very_low_frequency#Amateur_use